1. Field of the Invention
The present invention relates to a method and structure for preventing slipping-off of a tube in a pipe joint made of resin, and more particularly to a method and structure for preventing slipping-off of a tube in a pipe joint made of resin which is preferably used in piping for a liquid having high purity or ultrapure water to be handled in a production process in, for example, production of semiconductor devices, production of medical equipment and medicines, food processing, and chemical industry.
2. Description of the Prior Art
As a pipe joint made of resin of this kind, for example, known is a pipe joint shown in FIG. 8 (for example, Japanese Utility Model Publication No. 7-20471). The pipe joint made of resin comprises a joint body 1 and a union nut 2 which are made of resin such as fluororesin having excellent heat resistance and chemical resistance. An inner ring 4 is pressingly inserted into one end portion 3a of a tube 3 which is to be inserted into joint body 1 to be connected thereto, and which is the made of resin such as fluororesin.
In the joint body 1, a receiving port 6 is formed at least in one end of a cylindrical body portion 5, a first primary sealing portion 7 is formed in an inner area of the receiving port 6 so that the sealing portion intersects the axis C of the joint body 1, and a secondary sealing portion 8 is formed in an entrance area of the receiving port 6 so that the sealing portion intersect the axis C. An external thread portion 9 is formed on the outer periphery of the receiving port 6. The inner diameter of the receiving port 6 is larger than that of the body portion 5. In the inner area of the receiving port 6, the first primary sealing portion 7 is formed by a tapered face which is smaller in diameter as further moving toward the outer side in the axial direction and then reaches the inner radial face of the body portion 5. On the other hand, the secondary sealing portion 8 is formed by a tapered face which is larger in diameter as further moving from the inner area of the receiving port 6 toward the outer side in the axial direction and then reaches the end face of the receiving port 6.
The inner ring 4 is a molded piece of resin such as fluororesin. In the inner ring, a protruding portion 10 having an outer diameter that allows the portion to be fitted into the receiving port 6 of the joint body 1 is formed in an inner end portion in the axial direction, and a press insertion portion 11 which is to be pressingly inserted into the one end portion 3a of the tube 3 is formed in an outer end portion in the axial direction, thereby shaping the inner ring into a sleeve-like shape as a whole. An inner end sealing portion 12 which abuts against the first primary sealing portion 7, and which is configured as a tapered face is formed in the inner end face of the protruding portion 10. The press insertion portion 11 consists of a bulge portion 11a, and a connecting portion 11b which connects the bulge portion 11a to the protruding portion 10. The outer diameter of the connecting portion 11b is set to be smaller than that of the protruding portion 10 by a degree corresponding to the thickness of the tube 3. The bulge portion 11a is formed into a mountain-like section shape having: a tapered outer end sealing portion 13 which is larger in diameter as further moving from the outer end in the axial direction and toward the inner side; and a tapered face 15 which is smaller in diameter as further moving from the apex of the outer end sealing portion 13 toward the connecting portion 11b. The outer diameter of the apex of the outer end sealing portion 13, i.e., the maximum outer diameter of the bulge portion 11a is set to be larger than the outer diameter of the connecting portion 11b. The tapered face 15 is formed so that the inclination angel is substantially equal to that of the secondary sealing portion 8 of the joint body 1, and, when the inner end sealing portion 12 abuts against the primary sealing portion 7, the gap through which the secondary sealing portion 8 is opposed to the tapered face 15 corresponds to the thickness of the tube 3. The inner diameter of the inner ring 4 is set to be equal to or substantially equal to the inner diameters of the tube 3 and the body portion 5 of the joint body 1, so as not to impede movement (flow) of a fluid.
The inner ring 4 is pressingly inserted into the one end portion 3a of the tube 3 under a state where the protruding portion 10 is outwardly projected, whereby the diameter of the one end portion 3a of the tube 3 is increased to form a diameter-increased portion 16, and also to form a diameter-increased root portion 17 in a place where an opposite-insertion direction side inclination 16a of the diameter-increased portion 16 on the side opposite to the direction of insertion into the joint body 1, and a tube outer face 30 which is parallel to the tube axial direction meet each other.
Under the state where the one end portion 3a of the tube 3 is inserted into the receiving port 6, the inner end sealing portion 12 abuts against the first primary sealing portion 7 of the joint body 1, and the outer end sealing portion 13 abuts against the inner face of the opposite-insertion direction side inclination 16a serving as a second primary sealing portion of the diameter-increased portion 16 of the tube 3. The one end portion 3a of the tube 3 is clamped in an inclined state between the secondary sealing portion 8 of the joint body 1 and the tapered face 15 of the inner ring 4. Namely, an insertion direction side inclination 16b of the diameter-increased portion 16 of the tube 3 which is deformed along the tapered face 15 of the inner ring 4 abuts against the secondary sealing portion 8.
In the union nut 2, an internal thread portion 18 which is to be screwed to the external thread portion 9 of the joint body 1 is formed on the inner peripheral face, an annular flange portion 19 is inward projected from one end, and a pressing edge portion 19a of an acute angle or a right angle is formed on the inner end in the axial direction of the inner peripheral face of the flange portion 19.
Under the state where the one end portion 3a of the tube 3 into which the inner ring 4 is pressingly inserted is inserted into the receiving port 6 of the joint body 1, the internal thread portion 18 of the union nut 2 which is previously loosely fitted onto the outer periphery of the one end portion 3a is screw-fastened to the external thread portion 9 of the joint body 1. As a result of this fastening, the pressing edge portion 19a of the union nut 2 abuts against the diameter-increased root portion 17 of the diameter-increased portion 16 of the tube 3 to press the inner ring 4 in the axial direction. As a result, the inner end sealing portion 12 of the inner ring 4, and the insertion direction side inclination 16b of the tube 3 are pressingly contacted with the primary sealing portion 7 of the receiving port 6 of the joint body 1 and the secondary sealing portion 8 of the tube 3, respectively, and the inner face of the opposite-insertion direction side inclination 16a serving as the second primary sealing portion of the tube 3 is pressingly contacted with the outer end sealing portion 13 of the inner ring 4, whereby the sealing property (sealing force) is exerted and at the same time the tube 3 is prevented from slipping off.
In the pipe joint made of resin in which the fastening of the union nut 2 causes the pressing edge portion 19a to abut against the diameter-increased root portion 17 of the diameter-increased portion 16 of the tube 3, thereby pressing the one end portion 3a of the tube 3 together with the inner ring 4 against the joint body 1, the diameter-increased root portion 17 of the diameter-increased portion 16 of the tube 3 is simply rounded in a gentle manner. Therefore, sliding of the pressing edge portion 19a occurs. Particularly, the union nut 2 and the tube 3 which are made of fluororesin have a low coefficient of friction, and hence easily slide. Consequently, these components exert a small resistance against pulling-out of the tube 3, and there is the possibility that the tube slips off. In order to increase the pulling resistance of the tube 3, the union nut 2 is firmly fastened, and the force of pulling the tube 3 is maintained by the fastening force.
With respect to the pulling resistance against the fluid pressure which is applied to the tube 3 in a usual use, the above-mentioned structure of a pipe joint does not cause any problem. In the case where the temperature of transported fluid exceeds a usual service temperature, the case where an abnormal fluid pressure is applied to the tube under severe service conditions in which the fluid pressure is very higher than that in a usual use, or the case where a mechanical pulling force other than the internal pressure is abnormally applied to the tube, it is critically important to ensure the safety particularly in transportation of hazardous chemicals. In the above-mentioned structure of a pipe joint made of resin, the pulling resistance of the tube 3 depends on the fastening force of the union nut 2. In this situation, a safety problem may be caused when the fastening force is lowered due to an error in an initial working process or changes with time. It is very important to consider the problems.
It is an object of the invention to provide a method and structure for preventing slipping-off of a tube in such a pipe joint made of resin in which means for preventing slipping-off of the tube is improved so that, even when an abnormal fluid pressure or an abnormal mechanical pulling force other than the internal pressure is applied to the tube, the function of preventing slipping-off of the tube, and the sealing function can be sufficiently exerted to ensure the safety.
Hereinafter, the method and structure for preventing slipping-off of a tube in a pipe joint made of resin according to the invention will be described with reference to the accompanying drawings. In the following description, the reference numerals are used in order to facilitate the understanding of the invention. The use of the reference numerals is not intended as restricting the invention to the illustrated example.
In the method of preventing slipping-off of a tube in a pipe joint made of resin according to the invention, a joint body (1) which has a receiving port (6) in one end portion, and in which an external thread portion (9) is disposed on an outer periphery of the receiving port; a tube (3) made of resin; and a union nut (2) which is loosely fitted onto an outer periphery of the tube, and in which an internal thread portion (18) that is to be screwed to the external thread portion (9) of the joint body (1) is disposed on an inner periphery, an annular flange portion (19) that is inward projected is disposed on one end, and a pressing edge portion (19a) is disposed in an inner diameter portion of the flange portion are prepared. One end portion of the tube (3) is inserted into the receiving port (6) of the joint body (1) in a state where a diameter-increased portion (16) is formed and a diameter-increased root portion (17) where an opposite-insertion direction side inclination (16a) of the diameter-increased portion meets a tube outer face (30) which is parallel to an axial direction of the tube is formed. The internal thread portion (18) of the union nut (2) is screw-fastened to the external thread portion (9) to cause the pressing edge portion (19a) to abut against the diameter-increased root portion (17) of the tube (3), thereby pressing the one end portion of the tube (3) toward the joint body (1). Before the union nut (2) is fastened, a recess (20) is previously shaped in the diameter-increased root portion (17) of the tube (3) against which the pressing edge portion (19a) is to abut, the recess being smaller in radius of curvature or angle than the diameter-increased root portion.
In a preferred embodiment, in the method of preventing slipping-off of a tube according to the invention, the diameter-increased portion (16) of the tube (3) is formed by pressingly inserting an inner ring (4) into the one end portion of the tube (3). Alternatively, the diameter-increased portion (16) of the tube (3) is formed by flaring the one end portion of the tube (3), and pressingly fitted onto an outer periphery of an end portion of the receiving port (6) of the joint body (1), the end portion being more forward than the external thread portion (9). Alternatively, the recess (20) is shaped into a curved portion (21) which is drawn by a radius of curvature that is smaller than a radius of curvature of the diameter-increased root portion (17), or into a corner (22) of an angle that is smaller than an angle of the diameter-increased root portion (17).
In the method of preventing slipping-off of a tube according to the invention, the recess (20) which is smaller in radius of curvature or angle than the diameter-increased root portion (17) of the diameter-increased portion (16) of the tube (3) is previously shaped in the diameter-increased root portion (17), and the pressing edge portion (19a) of the union nut (2) is then caused to abut against the recess. In accordance with the fastening of the union nut (2), therefore, the pressing edge portion (19a) can be always caused to stably and surely abut against and engage with the diameter-increased root portion (17) of the tube (3) without sliding thereover, so that a strong pressing force can be applied. Furthermore, the pulling resistance can be increased independent of the fastening force of the union nut (2). Even when the fastening force of the union nut (2) is lowered due to an error in a working process or changes with time, it is possible to avoid an accident of slipping-off of the tube which is most dangerous.
The structure for preventing slipping-off of a tube in a pipe joint made of resin according to the invention comprises: a joint body (1) which has a receiving port (6) in one end portion, and an external thread portion (9) on an outer periphery of the receiving port; a tube (3) made of resin; and a union nut (2) which is loosely fitted onto the outer periphery of the tube, and in which an internal thread portion (18) that is to be screwed to the external thread portion (9) of the joint body (1) is disposed on an inner periphery, an annular flange portion (19) that is inward projected is disposed on one end, and a pressing edge portion (19a) is disposed in an inner diameter portion of the flange portion. One end portion of the tube (3) is inserted into the receiving port (6) of the joint body (1) in a state where a diameter-increased portion (16) is formed and a diameter-increased root portion (17) where an opposite-insertion direction side inclination (16a) of the diameter-increased portion meets a tube outer face (30) which is parallel to an axial direction of the tube is formed. A recess (20) is shaped in the diameter-increased root portion (17) of the tube (3), the recess being smaller in radius of curvature or angle than the diameter-increased root portion. The internal thread portion (18) of the union nut (2) is screw-fastened to the external thread portion (9) to cause the pressing edge portion (19a) to abut against the recess (20) of the tube (3), thereby pressing the one end portion of the tube (3) toward the joint body (1).
In a preferred embodiment, in the structure for preventing slipping-off of a tube according to the invention, the diameter-increased portion (16) of the tube (3) is formed by pressingly inserting an inner ring (4) into the one end portion of the tube (3). Alternatively, the diameter-increased portion (16) of the tube (3) is formed by flaring the one end portion of the tube (3), and pressingly fitted onto an outer periphery of an end portion of the receiving port (6) of the joint body (1), the end portion being more forward than the external thread portion (9). Alternatively, the recess (20) is shaped into a curved portion (21) which is drawn by a radius of curvature that is smaller than a radius of curvature of the diameter-increased root portion (17), or into a corner (22) of an angle that is smaller than an angle of the diameter-increased root portion (17).
In the structure for preventing slipping-off of a tube according to the invention, the recess (20) which is smaller in radius of curvature or angle than the diameter-increased root portion (17) of the diameter-increased portion (16) of the tube (3) is shaped in the diameter-increased root portion (17), and the pressing edge portion (19a) of the union nut (2) abuts against the recess. In accordance with the fastening of the union nut (2), therefore, the pressing edge portion (19a) can be always caused to stably and surely abut against and engage with the diameter-increased root portion (17) of the tube (3) without sliding thereover, so that a strong pressing force can be applied. Furthermore, the pulling resistance can be increased independent of the fastening force of the union nut (2). Even when the fastening force of the union nut (2) is lowered due to an error in a working process or changes with time, therefore, it is possible to avoid an accident of slipping-off the tube which is most dangerous.
As described above, according to the invention, the pressing edge portion can be always caused to stably and surely abut against and engage with the diameter-increased root portion of the tube in a slide-proof manner, to exert a strong pressing force, by the simple means in which the recess that is smaller in radius of curvature or angle than the diameter-increased root portion of the tube is shaped in the diameter-increased root portion and the pressing edge portion of the union nut abuts against the recess. Furthermore, the pulling resistance can be increased independent of the fastening force of the union nut. Therefore, the invention attains an effect that, even when the fastening force of the union nut is lowered due to an error in a working process or changes with time, it is possible to avoid an accident of slipping-off of the tube which is most dangerous.